Alloy coatings and method of applying



ALLOY COATINGS AND ME'IHQD F APPLYING Lowell D. Eubank, Richland, Wash,and Ernest R. Boiler, Marion, Ind., assignors to the United States ofAmerica as represented by the United States Atomic Energy Coission NoDrawing. Application April 12, 1945 Serial No. 588,060

14 Claims. (Cl. 2919-l-) This invention relates to the coating ofmetallic uranium.

An object of the invention is the provision of firmly adherentprotective coatings on metallic uranium. A further object is theprovision of such coatings suitable for use as bases for the applicationof other metal coatings.

In accordance with the present invention metallic uranium is providedwith a coating of uranium-aluminum alloy. The application of such acoating to uranium by dipping the uranium in a bath of molten aluminumresults in the formation of a relatively thick alloy coatingcharacterized by objectionable brittleness. However, coatings highlysatisfactory for a variety of purposes may be formed by dipping themetallic uranium in a molten metal bath comprising a major proportion ofzinc and a minor proportion of aluminum (by Weight).

The thickness of the uranium-aluminum alloy coating may be varied byvarying the proportion of aluminum in the coating bath. Thus extremelythin coatings may be applied by using a zinc coating bath containing anamount of aluminum in the neighborhood of 1% of the bath. For theapplication of thicker coatings, correspondingly higher proportions ofaluminum should be employed.

The invention is capable of a variety of applications.

The uranium just as it comes from the hot dipping bath is suitablycoated for many purposes. Such a product comprises a multiple layercoating in which the metallic uranium is coated with a firmly adherentlayer of uranium-aluminum alloy containing in the neighborhood of 70% to75% of uranium, to of aluminum and about 5% of zinc. These proportionsof aluminum and uranium correspond approximately to the known alloy, UAIOver this alloy layer firmly adherent to it is a Zinc layer whichcontains about the same proportion of aluminum as present in the coatingbath. The uranium-aluminum layer serves as a blocking layer with theresult that very little uranium finds its way into the zinc layer. Theamounts of uranium found in this layer have been of the order of onepercent.

For the preparation of multiple protective coatings by a single dipprocess, proportions of aluminum between about 5% and about 15% byweight in the coating bath have been found to be most satisfactory.Coatings applied from such coating baths include a layer ofuranium-aluminum alloy adequate to afford excellent protection for theuranium. Proportions of about 1% aluminum have been used in coatingbaths for the production of Zinc coatings useful for many purposesdespite the thinness of the alloy layer.

The invention has been found to be useful in bonding uranium to aluminumsheathing. Such sheathing may be bonded directly to the zinc layer byapplying the sheathing while the coating is still molten. Alternativelythe coated metal may be soldered to the aluminum by means of ordinaryaluminum solder (about 90% tin 2,848,796. Patented Aug. 26, 1958 and 10%zinc). Coatings applied by means of a molten bath of 99 parts by weightof zinc and one part by weight of aluminum have been found highlysatisfactory for such applications.

The coatings of the invention are useful as bonding coatings for theapplication of other metal coatings, such as coatings ofaluminum-silicon brazing and casting alloys, lead, and terne.

in cases where zinc coatings are undesirable, the uranium-aluminum alloycoating of the invention may be applied as described above and the zinclayer may be removed by centrifuging the coated article while yet hot orby subsequently treating the surface of the article with an acid, suchas nitric, sulfuric or hydrochloric acid, to dissolve the zinc, or bymechanically removing a portion of the solid coating so as to expose theuraniumaluminum alloy layer.

Some commercial grades of zinc, used alone, are not satisfactory forcoating uranium; thus Prime Western Spelter has been found to atfordonly spotty coverage. The present invention makes possible the use ofsuch grades of zinc to provide continuous adherent coatings.

Preferred temperatures for the application of the coatings of thepresent invention are temperatures between 20 and 200 centigrade degreesabove the melting point of the particular coating bath being applied.Thus higher temperatures are most suitable for baths of a compositionrelatively remote from the eutectic alloy composition (95% zinc, 5%aluminum) and lower temperatures are most suitable for alloys nearer tothis composition.

Before coating metallic uranium, it is desirable to prepare the uraniumsurface by a suitable pickling treatment. Pickling treatments whichhave'been found to be suitable are treatments in aqueous nitric acidhaving a concentration of about 50% HNO for a few minutes at atemperature between 60 and C. Other pickling procedures, for example,pickling by means of a sulfuric acid pickling reagent, have beenemployed with somewhat less satisfactory results. A pickling treatmentwhich has been found to be most satisfactory is the pickling treatmentdescribed in U. S. patent application Serial Number 619,265 of E. R.Boiler, Lowell D. Eubank and John W. Robinson filed September 28, 1945,and entitled Nitric Acid Pickling Process.

While treatment of the metal with a flux is not essential to theapplication of satisfactory coatings, it is sometimes desirable. Theapplication of a flux of the type described in U. S. patent applicationSerial Number 583,176 of Lowell D. Eubank filed March 16, 1945, andentitled Method of Flux-treating Metal Surfaces been. found be verysatisfactory. These fluxes comprise alkali-metal halides, preferablymixtures including lithium and potassium chlorides.

When a flux is employed, the uranium may be dipped first into the fluxand then into the coating bath, but it is preferred to employ the fluxas a protective layer on top of the coating bath and to dip the uraniumarticle through this flux into the bath. In this way possible exposureof the metal to air after withdrawal from the flux is avoided and theflux serves the dual function of protecting the coating bath andpreparing the surface to be coated.

After removing the article from the coating bath it may be cooled slowlyin air. Cylindrical bodies may be cooled to solidify the coating byrolling on smooth continuous rollers as described in U. S. patentapplication Serial Number 577,382 of Harold A. Gage, filed February 12,1945, and entitled Method of Leveling Metal Coatings.

When the coatings of the invention are used as bases for hot-dippedmetallic over-coatings, the latter may be applied while the zinc layeris still molten. Such coatings as well as electroplated coatings andnon-metallic coatings may be applied .to the coatings of the inventionafter they have solidified and either with or without removal of theouter zinc-aluminum alloy layer.

The following examples illustrate specific applications of theinvention. In the examples quantities areexpressed in terms of weightunless otherwise indicated.

Example 1 A metallic uranium rod, about 1.1 inch in diameter and 4inches long, was pickled in aqueous 50% nitric acid solution at 60-65 C.for three minutes. Following this it was rinsed in clean water andair-dried. It was then dipped through a flux consisting of 53% potassiumchloride, 42% lithium chloride, and sodium chloride into a molten bathcomprising 85 parts of zinc and 15 parts of aluminum, at 560 C., forthree minutes. The rod was withdrawn from the bath, shaken to removeexcess coating metal, and rolled. on Transite rollers until the coatingsolidified. The rod was then allowed to cool in air to room temperature.The coating was tested by placing the rod in a current of hot airmaintained at 200 C. for 40 days. At the end of this period the coatingwas perfect. The rod was then placed in a current of air at 250 C. After122 additional days the coating was still perfect, at which time thespecimen was removed from test.

Example 2 A metallic uranium rod about 1.1 inch in diameter by 4 incheslong was pickled in aqueous 50% HNO solution at about 65 C. for 2%minutes. It was then dipped through a flux comprising 53% KCl, 42% LiCl,and 5% IaCl into a molten bath comprising 85 parts of zinc (PrimeWestern Spelter) and 15 parts of aluminum at 530 C. for 4 minutes.

The rod was withdrawn from the bath, shaken to remove excess coatingmetal and rolled on Transite rollers until the coating solidified. Therod was then placed in an oven at 250 C. for 3 hours to allow the coatedrod to cool gradually to this temperature and then was allowed to coolin air to room temperature.

The coating was tested by placing the rod in a current of hot airmaintained at 200 C. for 59 days. At the end of this period the coatingwas still perfect. The rod was then placed in a current of air at 250 C.After 106 days more at this higher temperature the coating was stillfree from defects.

Example 3 A small metallic uranium article having a machined surface wasdipped in 50% HNO solution at between 60 and 65 C. for 2% minutes. Itwas then rinsed in water and wiped dry.

The article was next dipped through a top flux comprising 42% LiCl, 53%KCl and 5% NaCl into a molten zinc-aluminum bath containing 85 parts ofzinc (Prime Western Spelter) and 15 parts of aluminum, the bathtemperature being 600 C.

The article was withdrawn after 2 /2 minutes in the bath and rolled inair on carbon rollers for about 2 minutes to cause the coating tosolidify. The article was then dipped into a zinc bath at a temperatureof 450 C. for one minute. It was withdrawn from this bath and againplaced on carbon rollers where it was rolled until the coating hadsolidified (1 /2 minutes).

It was then placed in an annealing oven at a temperature of 248 C. andallowed to cool therein to this temperature. After remaining in the ovenfor about 2 /2 hours, it was inspected and found to be smooth and brightin appearance.

It was then tested by holding it in-contact with hot air at 200 C. After78 days of exposure, the coating was still in perfect condition.

Example 4 A metallic uranium rod of the same size and type as employedin Example 1 was pickled for 2 /2 minutes at 60 C. in 50% nitric acidsolution, rinsed in water and wiped dry.

it was then dipped through a top flux comprising 42% LiCl 53% KCl, and5% NaCl into a zinc-aluminum bath comprising parts of zinc (P. W. S.)and 15 parts of aluminum at a temperature of 600 C. After 2 /2 minutesthe rod was withdrawn from the bath and rolled for 2 minutes in air tocause the coating to solidify.

It was then placed in an annealing oven which Was maintained at atemperature between 250 and 260 C. for 2 /2 hours and finally allowed tocool in air to room temperature. The appearance of the rod was smoothand slightly dull.

The coated rod was placed in air at 200 C. to test the durability of thecoating. After 70 days of exposure th coating was still in perfectcondition.

Example 5 A small uranium rod about 1.1 inch in diameter and 4 inches inlength was pickled in nitric acid as in the preceding example, rinsedand dried.

It was then dipped into a fluxless molten metal bath comprising 85 partsof zinc (P. W. S.) and 15 parts of aluminum at a temperature of 560 C.and held in this bath for 3 minutes. It was removed from the bath andthen dipped for one minute in a fluxless molten terne bath comprising97.5 parts of lead and 2.5 parts of tin at a temperature of about 400 C.

The coated rod was cooled on smooth rotating rollers for 2 minutes andthen allowed to cool further in air to room temperature.

It was then placed in a hot air oven maintained at a temperature of 200C. After 7 days, the coating was still in perfect condition, and the rodwas removed from the oven and placed in a second oven at a temperatureof 250 C. in contact with air. After 30 days of exposure at 250 C., thecoating was still free from defects.

Example 6 A small uranium rod, after pickling as in the precedingexample, was dipped through a flux of 42% LiCl, 53% KCl and 5% NaCl intoa molten metal bath comprising 85 arts of zinc (Prime Western Spelter)and 15 parts of aluminum at 560 C. for 3 minutes.

It was then removed and dipped through a flux of the same compositioninto a molten metal bath comprising 88 parts of aluminum and 12 parts ofsilicon at 600 C. for one minute. It was withdrawn from this second bathand placed in an annealing oven at a temperature of 250 C. and allowedto cool to this temperature in a period of about 3 hours. It was thenwithdrawn and cooled in air to room temperature.

The durability of this coating was tested by placing the rod in a hotair stream at a temperature of 200 C. After 30 days of exposure, thecoating was examined and found to be still in perfect condition. It wasthen placed in a hot air stream at a temperature of 250 C. for anadditional 17 days. At the end of this period the coating was still freefrom defects.

Example 7 A metallic uranium rod inch in diameter and 2 inches in lengthwas dipped in an aqueous 50% HNO solution at about 65 C. for 3 minutes.It was then dipped through a flux of the composition 37% LiCl, 53% KCland 10% NaCl into a molten bath containing 94 parts of zinc (PrimeWestern Spelter) and 6 parts of aluminum at 485 C. V

The rod was withdrawn from the coating bath and rolled in air on carbonrollers for 2 minutes to allow the coating to solidify. It was thendipped in cold water to cool the rod to normal temperature.

The rod was then placed in an oven through which air at 200 C. wascirculated, to determine its resistance to corrosion. After 135 days ofthis treatment, the rod was still in perfect condition.

Example 8 A metallic uranium rod about 1.1 inch in diameter by 4 incheslong was pickled in aqueous 50% nitric acid solution at 60 C. for fiveminutes. Following this it was rinsed in clean water and air-dried. Itwas then dipped through a flux consisting of 53% potassium chloride, 42%lithium chloride, and 5% sodium chloride into a molten bath consistingof 85 parts of zinc and parts of aluminum at 530 C. for four minutes.The rod was withdrawn from the bath, shaken to remove excess coatingmetal and rolled on Transite rolls until the coating solidified. It wasallowed to cool to room temperature in air.

The outer coating of zinc-aluminum alloy was removed by immersing thecoated rod in 25% nitric acid at room temperature. This left asubstantially continuous uranium-aluminum alloy coating remaining on thespecimen. The alloy coating was tested by placing the rod in a currentof hot air at 300 C. At the end of 30 days a few pinholes had developedin the coating, the sum total of the areas involved amounting to lessthan 0.1% of the total coating. This rate of failure was comparable tothat normally obtained with specimens carrying the zincaluminumover-coating when tested under similar conditions.

Example 9 A metallic uranium rod about 1.36 inches in diameter by 8inches long was pickled in aqueous 50% HNO solution for five minutes at60 to 70 C., rinsed in flow ing water and dried. The rod was then dippedinto a bath of 99-1 Zn-Al alloy at 450475 C. for 1 /2 minutes and theninserted into an aluminum can held at 425 C., the aluminum can havingbeen previously coated with the Zn-Al alloy by brushing with the moltenalloy. A firm bond between the uranium rod and the aluminum can was thusobtained.

It will be understood that we intend to include variations andmodifications of the invention and that the preceding examples areillustrations only and in no wise to be construed as limitations uponthe invention, the scope of which is defined in the appended claims,wherein we claim:

1. A solid metallic uranium article having its surface protected by alayer of uranium-aluminum alloy.

2. A solid metallic uranium article having its surface protected by amultiple layer coating comprising a firmly adherent inner layer ofuranium-aluminum alloy and a second layer of zinc firmly bonded to theuranium-aluminum alloy.

3. A solid metallic uranium article having its surface protected by alayer of uranium-aluminum alloy of the approximate composition UA lcontaining about 5% of Z111C.

4. A solid metallic uranium article having its surface protected by amultiple layer coating comprising an inner layer of a uranium-aluminumalloy of the approximate composition UAl containing about 5% of zinc,firmly bonded to the uranium, and a layer of zinc firmly bonded to thealloy layer.

5. A solid metallic uranium article having its surface protected by amultiple layer coating comprising an inner layer of a uranium-aluminumalloy, a second layer of Zinc-aluminum alloy, and a third layer oflead-tin alloy.

6. The method of protectively coating solid metallic uranium, whichcomprises removing oxide film from the solid metallic uranium anddipping the solid metallic uranium into a molten metal bath comprisingabout 55 to 99 parts of zinc and 45 to 1 part of aluminum at atemperature between and 200 centigrade degrees above the melting pointof the metal bath.

7. The method of applying a multiple layer coating to solid metallicuranium, which comprises removing oxide film from the uranium, dippingthe solid metallic uranium in a molten metal bath comprising between 5and 15 parts of aluminum and between 95 and parts of Zinc at atemperature between 20 and 200 centigrade degrees above the meltingpoint of the metal bath, withdrawing the solid metallic uranium from themetal bath, and cooling the coated metallic uranium to cause the coatingto solidify.

8. The method of protectively coating metallic uranium, which comprisesapplying to the metallic uranium a coating of zinc containing aluminum,applying to the zinc-coated uranium a layer of molten lead containingtin, and causing the molten tin-containing lead to cool and solidify onthe zinc-coated uranium.

9. The method of applying a multiple layer coating to solid metallicuranium, which comprises removing oxide film from the uranium, dippingthe solid metallic uranium in a molten metal bath comprising between 5and 15 parts of aluminum and between and 85 parts of Zinc at atemperature between 20 and 200 centigrade degrees above the meltingpoint of the metal bath, withdrawing the solid metallic uranium from themetal bath, dipping the coated uranium while yet hot into a molten leadbath containing a minor proportion of tin and maintained at atemperature not substantially above the melting point of the Zincaluminum bath, subsequently withdrawing the coated uranium from the leadbath and cooling it to cause the coating to solidify thereon.

10. The method of protectively coating a metallic uranium rod ofcylindrical cross-section, which comprises removing oxide film from themetallic uranium rod, dipping the rod into a molten metal bathcomprising about 55 to 99 parts of zinc and 45 to one part of aluminumat a temperature between 20 and 200 centigrade degrees above the meltingpoint of the metal bath, withdrawing the rod and rolling it until thecoating solidifies.

11. The method of protectively coating a solid metallic uranium article,which comprises applying a molten metal solution of aluminum in zinc tothe solid metallic uranium article, said solution containing sufficientaluminum to react with the uranium under the prevailing conditions toform a protective layer of a aluminum-uranium alloy on the surface ofthe metallic uranium, withdrawing the coated article and dipping it intoa molten metal bath comprising an alloy of aluminum and silicon,withdrawing the coated article from the aluminum silicon alloy bath, andsubsequently cooling the article to cause the coating to solidifythereon.

12. The method of forming a protective uraniumaluminum alloy coating ona solid metallic uranium article which comprises removing oxide filmfrom the uranium, dipping the uranium into a molten bath comprisingabout 55 to 99 parts of zinc and 45 to 1 parts of aluminum at atemperature between 20 and 200 C. above the melting point of the metalbath, whereby a coating of uranium-aluminum alloy is formed upon thesurface of the uranium article and an outer coating of zinc is formedabout said uranium-aluminum coating, removing the article from the bathand thereafter removing the zinc layer.

13. The method of claim 12 wherein the zinc is removed by centrifugingthe coated article at a temperature greater than the melting point ofZinc.

14. The method of forming a protective uraniumaluminum alloy coating ona solid metallic uranium article which comprises removing oxide filmfrom the uranium, dipping the uranium into a molten bath comprisingabout 55 to 95 parts of zinc and about 45 to 1 parts of aluminum at atemperature between 20 and 200 C. above the melting point of the moltenbath whereby a coating of uranium-aluminum alloy is formed upon thesurface of the uranium article and an outer coating of zinc is formedabout said uranium-aluminum coating, removing the article from the bath,cooling the article to UNITED STATES PATENTS 943,161 Rockey 'Q Dec. 14,1909 1,378,052 Peacock May 17, 1921 1,764,132 Wehr June 17, 1930 8Austin Jan. 16, 1934 Liban Jan. 26, 1937 FOREIGN PATENTS Great BritainOct. 3, 1941 OTHER REFERENCES 1 Metal Cleaning and Finishing, Qctober1934, pp. 509- 512, 526,"A1uminum Improves Finish in Galvanizing byWallace G. Imhofl.

1. A SOLID METALLIC URANIUM ARTICLE HAVING ITS SURFACE PROTECTED BY ALAYER OF URANIUM-ALUMINUM ALLOY.
 6. THE METHOD OF PROTECTIVELY COATINGSOLID METALLIC URANIUM, WHICH COMPRISES REMOVING OXIDE FILM FROM THESOLID METALLIC URANIUM AND DIPPING THE SOLID METALLIC URANIUM INTO AMOLTEN METAL BATH COMPRISING ABOUT 55 TO 99 PARTS OF ZINC AND 45 TO 1PART OF ALUMINUM AT A TEMPERATURE BETWEEN 20 AND 200 CENTIGRADE DEGREESABOVE THE MELTING POINT OF THE METAL BATH.